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Phosphorylation of the Conditioning-Associated GTP-Binding Protein cp20 by Protein Kinase C

Authors

  • T. J. Nelson,

    Corresponding author
    1. Laboratory of Adaptive Systems, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, U.S.A.
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  • D. L. Alkon

    1. Laboratory of Adaptive Systems, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, U.S.A.
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Address correspondence and reprint requests to Dr. T. J. Nelson at Laboratory of Adaptive Systems, NINDS, NIH, Building 36, Room 4A-23, Bethesda, MD 20892-4124, U.S.A.

Abstract

Abstract: The phosphorylation state of cp20, a low molecular weight membrane-associated GTP-binding protein, was previously shown to increase two- to threefold 24 h after associative conditioning. Here, cp20 is shown to be phosphorylated by protein kinase C (PKC) in vitro. Pronounced differences in activity were observed with the three major isoforms of PKC, whereas casein kinase, calcium/calmodulin-dependent protein kinase II, and cyclic AMP-dependent protein kinase produced no detectable phosphorylation of cp20. Phosphorylation of cp20 had no effect on its GTPase or GTP-binding activity but caused a translocation of cp20 from cytosol to the nuclei/mitochondrial particulate fraction. These results suggest that the increase in phosphorylation of cp20 after conditioning may be due to PKC.

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